In gravure printing, a copper plated ink fountain cylinder is engraved to form an image in intaglio. The intaglio image is defined by cells or wells etched into the cylinder surface. Each cell is sized to contain a predetermined amount of ink. Ink is supplied to the cells by an ink fountain. As the cylinder rotates, the cells are flooded with ink and the surface between cells is wiped clean by a doctor blade. Ink is discharged from each cell and transferred to the smooth surface of an elastomeric blanket secured to a transfer cylinder. The blanket contacts a moving substrate such as a polyethelene film so as to transfer the inked image to the substrate.
Successive gravure stations may be operated in-line to form a multi-colored design comprising a vignette, line printing or any combination of the two. A vignette is a multicolored dot pattern which forms a facsimile of a transparency. Each station is supplied with its own ink fountain and transfer cylinders as well its own colored ink. The cells on an ink fountain cylinder are arranged in parallel lines. There is a predetermined number of lines per square inch depending on the fineness of the image. The line angle varies from one ink fountain cylinder to another to avoid objectionable visual effects in the inked image.
The flexographic printing process provides a simplified ink distribution system. In flexograph printing, an anilox or ink metering cylinder is etched mechanically with cells or wells using a knurled master cylinder. The metering cylinder is flooded with ink at the ink fountain. The cells are sized uniformly so that each contains a predetermined volume of ink. A metered amount of ink is accurately distributed by the cylinder to a flexographic printing plate mounted on a plate cylinder. The printing plate is made of an elastomeric material bearing an image in relief. Successive flexographic stations may be operated to form a design comprising a vignette, or line printing, or combination of both. Ink is deposited on the printing plate at each station by the metering cylinder, and the image is printed on the substrate by the printing plate.
In both the gravure and flexographic processes, a change in any portion of the substrate design requires replacement of an entire ink fountain cylinder or series of cylinders or an entire flexographic printing plate or series of printing plates.
The problem solved by the present invention is that of providing a quick and inexpensive way to change a specific vignette or line portion of a substrate design without having to replace an entire cylinder or printing plate, and without changing the remaining portions of the design.